Electromagnetic deflection yoke having bypassed winding turns

ABSTRACT

A DEFLECTION YOKE FOR A COLOR TELEVISION PICTURE TUBE IS PROVIDED THE COILS OF WHICH HAVE ELECTRICAL TAPS WHICH ARE CONNECTED SUCH THAT A PORTION OF THE COIL WINDINGS ARE BYPASSED   TO PROVIDE AN EFFECTIVE TURNS DISTRIBUTION MODIFICATION TO CONTROL THE ELECTRON BEAM MISCONVERGENCE.

United States Patent Robert Lloyd Barbin Indianapolis, Ind. [2|] Appl. No. 844,318

[22] Filed July 24, 1969 [45] Patented June 28, I971 [73] Assignee RCA Corporation [72] Inventor [54] ELECTROMAGNETIC DEFLECTION YOKE HAVING BYPASSED WINDING TURNS $Clalms,4 Drawing Figs.

52 use! 313/76, 3l5/27,335/2l3 s1 lnt.Cl I. ..l'l0lj29l76 [50] FieldofSearcli 313/75,?6,

[56] References Cited UNITED STATES PATENTS 2,l72,733 9/1939 Federmann et al 2,569,343 9/1951 Scull, Jr

3,169,207 2/1965 Obert et al .I:

Primary Examiner-Roy Lake Assistant Examiner-V. Lafranchi Attorney-Eugene M. Whitacre ABSTRACT: A deflection yoke for a color television picture tube is provided the coils of which have electrical taps which are connected such that a portion of the coil windings are bypassed to provide an effective turns distribution modification to control the electron beam misconvergence.

PATENTED M2 8197! INVIEN'IOR. Robert L. Barb/n AGENT ELECTROMAGNETIC DEFLECTION YOKE HAVING BYPASSED WINDING TURNS BACKGROUND OF THE INVENTION This invention relates to electromagnetic deflection yokes for color television picture tubes and particularly to yoke coils having tapped windings connected to achieve satisfactory convergence of the electron beams.

In a color television receiver utilizing a color picture tube having three electron beams to excite different colored phosphors on the viewed portion of the picture tube it is necessary that the three beams be properly converged as they are deflected over the entire viewed portion in order to provide an acceptable picture having good resolution. In a shadow mask type of color picture tube, for example, three electron beams are emitted from an electron gun structure having three electron guns disposed at the apices of an equilateral triangle and located in the neck portion of the picture tube. The electron beams are accelerated and converged to pass through small apertures in the mask after which the beams spread slightly to land upon and excite red, green and blue phosphor dots located on a phosphor screen in register with the mask apertures.

Due to the geometry of the shadow mask picture tube, the three electron beams do not intersect the plane of the screen as a circular bundle as the beams are deflected over the screen. It is usual to converge the beams by applying convergence correction waveforms at the line scanning and field scanning rates to electromagnetic pole pieces located around the neck portion of the tube to dynamically vary the radial position of the beams. In this manner the beams tend to fomi a circular bundle everywhere on the screen.

However, the convergence of the beams is also affected by the electromagnetic fields produced by the deflection yoke, including the characteristics of astigmatism and coma.

Astigmatism may be isotropic or anisotropic. Isotropic astigmatism is a characteristic of the independent vertical and horizontal deflection coils and the effects of each set of coils is linearly combined in the corners of the screen. The misconvergence caused by astigmatism may be corrected by modifying the on-axis (vertical and horizontal) convergence correction waveforms described above. Anisotropic astigmatism occurs only during simultaneous deflection by both pairs of deflection coils andeffects the beam bundle in the corners of the screen. Expensive circuitry for producing complicated correction waveforms is required to correct the misconvergence due to the anisotropic astigmatism, therefore, the more practical approach is to design a deflection yoke having minimum anisotropic astigmatism.

Coma has the effect of distorting symmetry of a-hypothetical conical beam bundle about an axis perpendicular to the direction of deflection. Due to the orientation of the three electron guns of a typical delta gun color tube (either blue gun up or blue gun down) the misconvergence caused by coma in the vertical coils can be corrected by modification of the vertical rate dynamic convergence waveform. However, coma in the horizontal coil is not completely controllable by the radial convergence waveforms, resulting in the blue raster being narrower or wider than the red and green rasters. Thismay be corrected with dynamic blue lateral devices but is more readily corrected by changing the magnetic field distribution of the horizontal deflection coil.

The electromagnetic field of the yoke coils may be altered to reduce the adverse effects of coma and astigmatism. In yokes employing saddle-type deflection coils the bulk of the active field-producing conductors disposed generally longitudinally of the tube may be shifted towards or away from the coil window to control the effects, including misconvergence, caused by coma and astigmatism.

The distortion of the beam bundle in the comers of the screen of a wide-angle picture tube is worse than in smaller deflection angle color picture tubes, and the design of a suitable deflection yoke is critical.

When a color receiver utilizes a wide angle color picture tube having a l 10 deflection angle, for example, the problems described above are present and in addition there are other problems including increased comer misconvergence caused by higher order electron optical aberrations. Among these are the horizontal spacing of the red and green vertical lines and the vertical misconvergence of the blue horizontal lines in the comer areas, and the vertical spacing between the red and green horizontal lines halfway to the corner when the axes and comers are converged. This corner misconvergence cannot be corrected by a simple shift of the bulk of the active coil conductors. These convergence errors are affected by the higher harmonics of the spatial turns distribution, or, by the transverse cross-sectional turns density at the start and finish of the coil winding compared to the middle. For wide deflection angles a relatively high turns density is required at the start and finish of the windings with respect to the center of the coil cross section.

An arbor in which the coils having the desired cross-sectional conductor distribution can be wound may be difficult or impractical to build because of considerations of arbor construction, strength and windability. In the past, one approach to achieve the desired turns distribution of the deflection coils is disclosed in U.S. Pat. No. 3,169,207 issued to M. J. Obert and R. L; Barbin and assigned to RCA Corporation. This patent discloses a yoke comprising coils with strands wound in multifilar fashion and with taps pulled from all strands in selected portions of the winding such that portions of the winding may be electrically connected in series and parallel arrangement. The connection of taps in this arrangement is complicated and the relatively long time required for this operation adds to the production cost of the yoke. Further, changing the electrical position of a tap in the multifilar strands to change the effective flux distribution of the winding changes the impedance of the yoke.

An object of this invention is to provide an improved deflection yoke for use with a color television picture tube for controlling the efiects of coma and astigmatism.

A deflection yoke is provided for a color television picture tube. The yoke comprises a pair of vertical and a pair of horizontal deflection coils, at least one pair of which has electrical taps formed in the windings and having the winding turns connected such that at least first and second portions of the windings adjacent the start and finish of the winding provide a path for deflection current waveforms applied thereto, and at least one portion of the winding turns located between the first and second portions is bypassed by the deflection current.

A more detailed description of the invention is given in the following specification and accompanying drawing of which:

FIG. 1 is a side view of a saddle-type deflection coil utilized in the yoke embodying the invention;

FIG. 2 is a top view of the deflection coil illustrated in FIG. 2;

FIG. 3 is a transverse cross-sectional view of the coil illustrated in FIG. 2 taken along the line 3-3 of FIG. 2; and

FIG. 4 is a schematic diagram of coil of a deflection yoke according to the invention.

DESCRIPTION OF THE INVENTION FIGS. l-3 illustrate a saddle-type coil used in a deflection yoke embodying the invention. The yoke comprises a pair of vertical and a pair of horizontal coils, the coils of each pair suitably mounted on opposite sides of and around the neck and bell-shaped portion of a color television picture tube in a known manner. Either or both pairs of coils may be made according to the invention but for illustrative purposes structure of a single coil will be described.

Deflection coil 10 is a saddle-type coil having two groups of active field-producing conductors 11 joined by groups of front and rear conductors 13 and 14, respectively. Conductor groups ll, 13 and 14 define a window area 12. A wire S represents the start of the winding adjacent the window area 12 and a wire F represents the end of the winding, referred to as the finish," and located on the bottom portion of coil 10.

Electrical taps T, and T, comprising wires 1",, and T, and T and T are shown near the center portion of coil between the start and finish turns. FIG. 4 illustrates schematically the interconnection of the portions of the coil 10 defined by the taps T and T, and start and finish turns S and F, respectively. The winding portion S-T comprising the turns located from the window towards the central portion of the coil transverse cross section, is serially connected to a portion T -F comprising the turns located from a central portion of the coil spaced from tap T to the finish turns F located farthest from the window area. A portion of the coil winding defined by the turns located between the tap wires T and T, in the central transverse cross section of the coil are bypassed and not connected to the field-producing turns. The unused wire ends T and T,,, are not connected to anything, or just one of them may be left connected to the other wire at its tap. A source of deflection current waveforms, not shown, is applied to the start and finish turns S and F to energize the coil.

The saddle-type coil winding described may be wound on conventional coil-winding apparatus embodying the teaching of US. Pat. No. 2,448,672 granted to H.V. Knauf on Sept. 7, 1948.

As mentioned previously, the corner convergence may be controlled by providing a deflection coil having a higher turns density at the ends of a transverse cross section relative to the turns density at the central portion of the coil cross section. In the embodiment described in conjunction with FIG. 1-4, no scanning current traverses the bypassed center portion of the winding, resulting in zero effective turns density in that area. Thus, the average turns density of the center portion is reduced relative to the end turns, providing the desired magnetic field for best corner convergence.

In a successfully operated embodiment of this invention, a

deflection yoke used in combination with a 19-inch diagonal delta gun shadow mask color picture tube having a ll0 deflection angle utilized horizontal coils having a total of 47 turns of eight strands of wire, with taps at the 25th and 27th turns.

One advantage flowing from a deflection yoke having coils according to the invention is the ease of compensating for different coil-winding arbors. An arbor may have to be replaced because of wear caused by the wire of many coils being passed over its surfaces. The replacement arbor may not have the identical shape as the original and therefore the coils produced by it will have different characteristics. In this situation the tapped portion of the coil may be moved towards or away from the window area, keeping the number of turns between the taps constant in accordance with the original design specification, to compensate for the variations in the arbor.

Also, the effects astigmatism and comma may be controlled by moving the fixed-turn winding portion between the taps towards or away from .the window area; the impedance of the yoke remaining constant because the total number of turns remains constant. This is important in that the coil driving circuitry will not have to be changed as the taps are moved.

Further, either a single strand of wire may be wound for forming the coil or multifilar strands may be utilized as the interconnection of the winding portions to bypass a central winding portion is simple, as illustrated in FIG. 4. Particularly in the case of a coil wound with multifilar strands, this method enables the coils to be produced more cheaply than the coils described in the aforementioned patent to Obert et al. because there are fewer interconnections to be made than in the prior art coils employing portions of the windings in a series-parallel arrangement.

I claim:

1. An electromagnetic deflection yoke for a color television picture tube comprising:

two pairs of saddle-type coils for deflecting the electron beams of said cathode ray tube along vertical and horizontal axes; the coils of at least one of said pairs comprising a plurality of turns of wire having electrical taps formed therein and connected such that at least first and second portions of said turns of wire disposed adjacent the start and finish of said coils are connected together to form a deflection current path and at least one portion of said turns disposed between said first and second portions is not connected to form a deflection current path. 2. An electromagnetic deflection yoke for a color television picture tube according to claim 1 wherein said coil wire comprises a single strand of wire.

3. An electromagnetic deflection yoke for a color television picture tube according to claim 1 wherein said coil wire comprises a plurality of strands of wire wound in a multifilar manner.

4. A deflection yoke for a shadow mask color television picture tube comprising:

a pair of saddle-type vertical deflection coils; a pair of saddle-type horizontal deflection coils; each of said coils comprising convolutions of wire forming two groups of active side conductors disposed generally longitudinally of said picture tube for deflecting the electron beams of said picture tube and front and rear end groups of inactive conductors disposed generally transversely of said picture tube joining said side conductors, said side conductors and end conductors defining a window area; each of said horizontal coils having electrical taps formed therein and connected such that a first portion of said side conductors adjacent said window and a second portion of said side conductors farthest from said window are serially connected to each other and the remaining portion of said side conductors between said taps in the central portion of said side conductor groups is not electrically connected to said first and second portions. 5. A method of winding saddle-type coils for use in a deflection yoke for a color television picture tube, said coils having a transverse cross-sectional conductor distribution with a higher turns density in coil portions adjacent and farthest from the window area of said coils relative to the turns density at a central portion of said coil cross section, comprising;

winding a first portion of said coil extending from the edge of said window area towards the central portion of a transverse cross section of said coil; forming a first electrical tap at the end of said first coil portion;

winding a second portion of said coil from said first tap extending to a second central portion of said transverse cross section of said coil;

forming a second electrical tap at the end of said second coil portion;

winding a third portion of said coil extending from said second tap to the end portion of said transverse cross section of said coil most remote from said window area; and

connecting said first and second taps such that said first and third coil portions are serially connected for providing a current path for deflection current waveforms applied to said coil and said second coil portion does not provide a conduction path for said deflection current waveforms,

said second coil portion being retained for providing support and displacement for said first and third coil portions. 

